The quince was another of my Mom's "secret ingredients" and it took us a good 20 minutes of googling and searching amongst other food bloggers' sites to figure out how to cook with one. Basically unless it is a very specific type of quince you must peel them and cook them, because they are bitter and very hard at the start.
We cooked ours twice and it still wasn't quite long enough. So if you're going to buy quince, just know that you should probably cook it longer than you'd expect. Lis simmered the quince and the pears in a cider and spice mix (which she can't for the life of her remember but she thinks it involved brown sugar and vanilla) until tender. Then she arranged the fruit on top of the pastry cream inside a pre-baked pastry shell and baked the whole tart again until the fruit was golden brown and caramelized.
It was a fantastic fall dish and I would highly recommend making up your own recipe for one. And if you want to learn more about quince I recommend Wikipedia (of course) and David Leibovitz.